The Modulatory Effect of Spatial Frequency on Audiovisual Emotional Integration: An ERP Study

Although the brain integrates multisensory inputs to assess emotions, the temporal neural dynamics of audiovisual affective processing for spatial frequency-modulated facial expression have yet to be clarified. Here, we employed event-related potentials to explore this issue. Participants performed an emotion categorization task, in which they judged happy, neutral, and fearful faces filtered into broad spatial frequency (BSF), high spatial frequency (HSF), or low spatial frequency (LSF) conditions, with stimuli presented in visual and audiovisual modalities. Behavioral results showed that the audiovisual facilitative effect depended on SF, being most pronounced for HSF and attenuated for BSF or LSF. Electrophysiological results revealed a threat-driven audiovisual emotion-perception process at the early sensory stage, whereby audiovisual enhancement was modulated by SF across emotions. At the P1 and N170 components, fearful stimuli elicited the strongest audiovisual enhancement across all SFs; neutral stimuli showed significant enhancement under both HSF and LSF, whereas happy stimuli exhibited facilitation exclusively at the P1 component under HSF conditions. In contrast, the early posterior negativity (EPN) audiovisual effect was sensitive to happy and neutral faces under BSF and LSF conditions. The late positive potential (LPP) revealed that audiovisual enhancement was interactively modulated by SF and emotion, with selective enhancement observed for happy faces under BSF, neutral faces under HSF, and fearful faces under both HSF and LSF conditions. These findings suggest that audiovisual emotion integration is tuned to distinctive SF contents across different emotional stimuli at different temporal processing stages, with early prioritization for threat-related stimuli.